We are continuing our studies on biotin in rats, chicks and other laboratory animals using the intact animal as well as various tissue preparations at the organ, cellular and subcellular level. (1) We are using biotin-deficient animals as a tool to investigate interrelationships, particularly the metabolic regulation of gluconeogenesis, lipolysis and ketogenesis versus glycolysis, glycogenesis and lipogenesis, and (2) we are studying synthesis in vitro of biotin holoenzymes from their apoproteins and biotin mediated by holoenzyme synthetases.